1. Field of the Invention
The present invention generally relates to a MIMO antenna device and an antenna package having the MIMO antenna device and, more particularly, to a MIMO antenna device that includes two antennas having a low correlation between the two antennas, as well as an antenna package having the MIMO antenna device.
2. Description of the Related Art
System in Package (SiP) technology has been widely used in multi-mode wireless communication products to integrate semiconductor chips with passive elements. As an example, passive elements such as electronic circuits, antennas and connectors are integrated as an integrated passive device (IPD) via semiconductor manufacturing technology.
As the demanded wireless transmission data rates continue to grow in the latest wireless communication technologies, such as Long-term evolution (LTE) and WiMAX, the conventional single-input and single-output (SISO) antenna technology is not a preferred choice to the users due to the limited channel capacity. In light of this, multi-input and multi-output (MIMO) antenna technology was proposed to replace the SISO antenna technology. The MIMO antenna technology allows multiple signals that are transmitted by emitting ends to be received through multiple receiving ends, significantly increasing the data throughput. Thus, the spectrum efficiency can be improved without increasing the bandwidth and the noise-signal ratio. In addition, antenna correlation is proportional to the S21 parameter and can be lowered by enhancing the antenna isolation. However, the MIMO antenna technology still has some drawbacks.
For instance, the antenna technologies disclosed in Taiwan Patent Publication No. 200952251 and U.S. Pat. Nos. 6,770,955, 8,058,714 and 7,944,038 are suitable for use in a single-antenna environment only. The antenna technology disclosed in Taiwan Patent No. M349047 is criticized for inconvenient integration of the antenna and the IC modules. In the antenna technologies disclosed in U.S. Pat. Nos. 6,239,752, 6,373,447, 6818985 and 6914566, the electromagnetic distributions between the antenna and the IC chip are not shown and described, making it difficult to obtain the actual isolation between the antenna and the IC chip. The antenna technology disclosed in U.S. Pat. Nos. 7,342,299, 7,352,056, 7,791,539, 7,880,677, 6,426,723, 7,408,511, 7,411,554, 7,473,433, 8,085,202 and 7,812,768, as well as in Taiwan Patent No. 1316310, cannot be used in a small-sized package system since the antennas take up (or occupy) larger spaces when the operational frequency is lower. In the antenna technologies disclosed in U.S. Pat. No. 7,408,511 and Taiwan Patent Nos. M418410, 1348250 and 201205957, the correlations of the antennas must be maintained by changing the antenna placement, increasing the ground areas of the antennas, keeping a certain gap between the antennas, or using decoupling circuits. In the antenna technologies disclosed in U.S. Pat. Nos. 7,352,328, 7,460,069 and 20090009400, the antenna isolations are maintained only when the antennas have certain gaps or when isolation devices are used.
In summary, apart from the disadvantages that the conventional antenna technologies require larger package dimensions and cannot be used in a multi-antenna environment, the conventional antenna technologies also have another disadvantage that the correlations or isolations of the antennas are maintained only by changing the antenna placement, increasing the ground areas of the antenna, or using the decoupling circuits or the isolation devices. This results in an inconvenient usage.
Thus, it is necessary to overcome the above problems by providing a MIMO antenna device that dose not require the match circuits, takes up a smaller space and has an outstanding isolation.